As is well known in the art, color images can be formed by imagewise exposure of a silver halide photographic light-sensitive material followed by color development whereby the oxidation product of the aromatic primary amine developing agent reacts with a dye-forming coupler.
Generally speaking, this color image forming method is based on the subtractive color reproduction principle, with cyan, magenta and yellow color images, each of which is in a complementary relationship to red, green and blue light, respectively, being produced. For example, cyan dye images are generally produced from couplers comprising phenol or naphthol derivatives. In the color photographic method, a color forming coupler is added to a developer solution or incorporated in a light-sensitive photographic emulsion layer or other color image-forming layer and reacts with the oxidation product of a color developing agent which is formed upon development to provide a non-diffusible dye. The reaction between the coupler and the color developing agent takes place at the active site(s) of the coupler. One mol of a so-called "4-equivalent coupler", in which all of the active sites are substituted with hydrogen, theoretically requires, on a stoichiometric basis, 4 mols of silver halide having developing nuclei as an oxidizing agent to form 1 mol of a dye.
On the other hand, 2-equivalent couplers are also known, having substituents releasable as anions at the active sites which require only 2 mols of silver halide having developing nuclei. Accordingly, by the use of 2-equivalent couplers, the amount of silver halide in the light-sensitive layer can be generally reduced and, hence, the coating thickness thereof can be reduced. This, in turn, enables the processing time of the light-sensitive material to be decreased and simultaneously results in the sharpness of the resulting color images being advantageously improved.
A variety of such coupling releasable groups are known including, for example, the sulfonamido groups set forth in U.S. Pat. No. 3,737,316, the imide groups set forth in U.S. Pat. No. 3,749,735, the sulfonyl groups set forth in U.S. Pat. No. 3,622,328, the aryloxy groups set forth in U.S. Pat. No. 3,476,563, the acyloxy groups set forth in U.S. Pat. No. 3,311,476, the thiocyano groups set forth in U.S. Pat. No. 3,214,437, the isothiocyanate groups set forth in U.S. Pat. No. 4,032,345, the sulfonyloxy groups set forth in U.S. Pat. No. 4,046,573, the thiocarbonyloxy groups set forth in Japanese Patent Application (OPI) No. 51939/77 (the term "OPI" as used herein refers to a "published unexamined Japanese patent application"), the aralkenylcarbonyloxy groups set forth in Japanese Patent Application (OPI) Nos. 39126/78 and 39745/78, the S-substituted monothiocarbonyloxy groups set forth in Japanese Patent Application (OPI) No. 45524/78, the propioroyloxy groups set forth in Japanese Patent Application (OPI) No. 47827/78, the ##STR1## groups set forth in U.S. Pat. No. 4,072,525, and the substituted alkoxy groups set forth in U.S. Pat. Nos. 3,227,551 and 4,052,212, Japanese Patent Application (OPI) Nos. 120334/75, 18315/77, 90932/77, 52423/78, 99938/78, 10522/78, 14736/79, 48237/79 and 66129/79.
Further, if the coupler contains a suitable type of coupling releasable group, for example, one which forms a diffusible dye structure, such a coupler, referred to as a diffusible dye-releasing coupler, can be employed in a diffusion transfer process in which the released dye is used to provide a dye image in an image-receiving layer. Diffusible dye-releasing couplers are described in, for example, U.S. Pat. Nos. 3,227,550, 3,765,886, U.S. Defensive Publication T900,029, British Pat. No. 1,330,524, etc. In addition, certain 2-equivalent colored couplers exhibit a masking effect to correct undesirable absorptions of dyes and such couplers are called colored couplers as described in, for example, Japanese Patent Application (OPI) No. 26034/76.
Furthermore, 2-equivalent couplers releasing a compound having a development suppressing effect, which are referred to as development inhibitor-releasing couplers, are also known. Since these couplers can suppress or inhibit development in proportion to the amount of the developed silver, these couplers are quite effective in reducing the image-forming particle size, gradation control, and improving color reproduction characteristics. These couplers can also be used in a diffusion transfer process to affect a layer adjacent to the layer in which they are present. Examples of these couplers are described in U.S. Pat. No. 3,227,554, Japanese Patent Application (OPI) No. 122335/74 and West German Patent Application (OLS) No. 2,414,006.
Since 2-equivalent couplers generally have certain advantages and a wider range of applications as compared with 4-equivalent couplers, the photographic industry tends to use 2-equivalent couplers more frequently.
However, most known 2-equivalent cyan color-forming couplers have certain disadvantages, in that the coupling reactivity is insufficient, color fog is formed, the dispersibility thereof is poor which causes difficulties during coating, the compound per se is unstable and cannot be stored for a long time, and the storage stability of the resulting color image formed by color development is poor. Thus improvements to overcome these disadvantages have been desired.